The present invention relates to an angular rate sensor used for an attitude controller and navigation system of a moving body such as an aircraft, an automobile, a robot, a ship, a vehicle or the like, a hand-movement compensator of a still camera, a video camera or the like, or a remote controller.
In an angular rate sensor of the above kind, a U-shaped piezoelectric element is provided with driving electrodes and sensor electrodes, and tuning fork prongs of the piezoelectric element are driven by a signal supplied by a single driving power supply connected to the driving electrodes. While they are being driven, an angular rate signal is output from the sensor electrodes.
In recent years, there have been suggested angular rate sensors that use mono-quartz piezoelectric elements such as crystallized quartz, lithium-tantalate, and the like as vibrating members. According to these suggestions, there is the possibility of supplying a smaller and less expensive angular rate sensor than the conventional angular rate sensor having a structure that comprises a piezoelectric element made of ceramic bonded to a vibrator of metallic material.
In the angular rate sensor of the prior art that uses a mono-quartz piezoelectric element, a tuning fork vibrator is composed of a pair of prongs connected firmly at one of their ends with a base. In some instances, they are of a one-piece structure, which is cut out from a quartz plate. The tuning fork vibrator constructed as above is provided with a pair of driving electrodes disposed to one of the prongs in an orientation of its major surfaces for driving the tuning fork vibrator piezoelectrically at the resonance frequency. The tuning fork vibrator is driven electrically by an external oscillator circuit. There are also provided on the other prong a monitor electrode for detecting amplitude of vibration of this tuning fork vibrator produced by the oscillator circuit, a sensor electrode for piezoelectrically detecting a stress produced by the Coriolis"" force acting on the prong in a direction orthogonal to its major surfaces responsive to an angular rate impressed around an axis of the tuning fork vibrator, and a ground electrode.
An electric charge generated in the:monitor electrode is amplified by an external circuit. Thereafter, the oscillator circuit is controlled by an AGC (automatic gain controller) in a manner that the vibration amplitude of the tuning fork vibrator becomes constant by comparing it with a pre-established reference signal. On the other hand, a signal produced by the Coriolis"" force and output by the sensor electrode is amplified first by an external amplifier circuit. It is then detected in a synchronized vibration of the tuning fork detected by the monitor electrode, so as to demodulate the signal by the Coriolis"" force, which is modulated by the tuning fork vibrator. A sensor output is produced after undesired signals within a band are cut off by an LPF (low pass filter).
In the angular rate sensor constructed as above, however, another circuit is required to separate a mixed-in signal, because there exists a coupling of a capacitive component induced in the sensor electrode by the driving signal. Since the mixed-in signal is not completely separable, it gives rise to a problem that a portion of the signal always remains. This has acted as undesired signal noises to degrade detecting performance of the sensor, and prevented it from practical use on a full-scale basis.
The present invention is intended to provide an angular rate sensor capable of obviating an influence of the above-stated undesired noises originating from the coupling of capacitive component, thereby improving the detecting performance.
In order to solve the problem, an angular rate sensor of this invention includes a first vibrator having at least two prongs and at least one base connecting the prongs composed of mono-quartz piezoelectric material, and a second vibrator composed of mono-quartz piezoelectric material in a shape generally similar to that of the first vibrator. The first vibrator and the second vibrator are directly bonded into one piece in an orientation of crystallographic axis that produces the piezoelectric phenomenon of reversed polarity with respect to each other in a lateral direction of the vibrators, and also in an orientation of their thickness, so as to form a tuning fork vibrator having at least two tuning fork prongs and at least one tuning fork base. The tuning fork vibrator is provided with a first electrode and a second electrode on front surfaces of its both prongs, and a third electrode and a fourth electrode disposed to back surfaces of the tuning fork prongs. The tuning fork vibrator is also provided with a fifth, a sixth, a seventh and an eighth electrodes formed as sensor electrodes on surfaces in a driving direction of the two tuning fork prongs. Any one of the first electrode provided on the front surface of one tuning fork prong of the tuning fork vibrator and the third electrode provided on the back surface of the same tuning fork prong is used as a driving electrode. Also, any one of the second electrode provided on the front surface of the other tuning fork prong and the fourth electrode provided on the back surface of the same other tuning fork prong is used as another driving electrode. A driving power supply is connected to supply driving signals of different phases between both of these driving electrodes. Among the above-said sensor electrodes, the fifth electrode and the eighth electrode provided on exterior-side surfaces of the two tuning fork prongs are commonly connected together, and the sixth electrode and the seventh electrode provided on interior-side surfaces of the tuning fork prongs are also commonly connected together. Thus they are so constructed that a sensor signal is tapped from these commonly connected points.
In the angular rate sensor of the described structure, unnecessary couplings of capacitive component can be cancelled out among the individual sensor electrodes, since these unnecessary couplings of capacitive component are produced equally between positive and negative polarities from the driving electrodes to the sensor electrodes, thereby obviating an influence of the noises originating in the couplings of capacitive component, and improving the detecting performance.